The goal of the proposed project is to assemble a collection of optimized immunogens based on the complete set of human transcription factors. These immunogens will be used by others to create renewable affinity reagents such as monoclonal antibodies. An initial, high priority appiication envisioned for such reagents is chromatin immunoprecipitation studies, and our aim is to design our immunogens so as to optimize them for this purpose. We will do this primarily using two strategies: (a) we will express transcription factor domains that flank the DNA recognition domain but do not overlap it in order to minimize inducing antibodies that might interfere with chromatin binding; and (b) wherever possible we will focus on transcription factor flanking domains that fold into complex three dimensional structures (native folds) and thus present highly specific 3D epitopes. We already have a protein production pipeline up and running that is producing > 1000 purified protein samples (including hundreds of human proteins) per year at the multi- milligram scale, so we are highly experienced in the relevant technologies, and meeting the goals of this FOA will require adding only a modest amount of extra capacity. We also have specialized software tools for the sophisticated analysis of human transcription factor sequences and the design of appropriate expression constructs. Our experience has shown that paying attention to the proper curation of genes and construct design at the beginning pays dividends downstream in terms of timely and cost-effective protein production because it minimizes wasting expensive wet lab resources on sub-par targets. Finally, we have a range of adaptable expression technologies that can be tailored to other classes of human protein targets (including secreted and membrane-bound proteins) in the future, so our approach is highly amenable to expressing additional sectors of the human proteome beyond transcription factors. RELEVANCE (See instmctions): The human genome project gave us a complete blueprint for the genetic instructions that control human biology. This proposal concerns a special set of human proteins known as transcription factors, which are the master effector.proteins in the cell that have the job of interpreting these instructions and telling the cell what to do under all sets of conditions. In diseases such as cancer these instructions can become garbled, which is why it is important to understand how transcription factors work. This proposal concerns the creation of a specific collection of human transcription factor-derived proteins that will allow scientists to precisely interrogate which transcription factors address which sets of instructions under a variety of conditions, thus establishing the outlines of the master control circuits in human cells.